1. Field of the Invention
The present invention relates to a magnetic tape cassette and more particularly to a magnetic tape cassette having a reel on which magnetic tape is wound and a takeup reel.
2. Description of the Prior Art
Recently, cassette tape recorders have been proposed which are miniaturized and light-weight and use a miniaturized magnetic tape. The magnetic tape received within the cassette of this type should provide recording and reproduction of high density for a long period of time. In order to fulfill the needs noted above, tapes such as the so-called C-120, C-100 tapes and the like are proposed. Moreover, to achieve higher density recording, the surface of a recording medium must be treated with a mirror face finish.
In a well known guide mechanism for guiding a cassette tape as shown in FIG. 1, if the tape has a good surface and is thin, such as noted above, the tape often becomes curled up dishwise or stepwise, in the case where the coefficient of sliding friction between layers of a recording surface of the tape and a backing material of the adjacent turn of the tape on the reel is large, e.g., more than 0.4, or if a layer of air in the space between the layers cannot be removed. This results in the occurrence of a loop or jamming as well as deformation of the tape itself, and in the worst case, causes stoppage of tape travel. This tendency is marked as the speed of tape increases.
As shown in FIG. 1, a well known tape travel guide mechanism for a cassette tape comprises a pair of reels 2 and 3 encased in a hollow case 1 formed by fixing an upper case 1a and a lower case 1b by means of fixing members 1c, a round rod like fixed pin 4, a rotary guide roller 5, a pressing pad 6, a rotary guide roller 7, a round rod like fixed pin 8, and a pair of flat guide plates 9 (only one shown in FIG. 1) disposed between the inner sides of said upper case 1a and lower case 1b and the opposite sides, respectively, of said reels 2 and 3.
Tape T, wound on the reel 2, is fed to the reel 3 orderly passing through the fixed pin 4, rotary guide roller 5, pressing pad 6 for urging tape T against a recording and reproducing head, rotary guide roller 7, and fixed pin 8, in such a manner that opposite edge portions of the tape are guided by the guide plates 9 so as to prevent displacement of the tape in the direction of the width of the tape T.
However, the prior art cassette as previously mentioned poses a drawback such that when the tape T is quickly reversed in its travel direction the relatively great contact angle of the tape and fixed pin causes increased tension. The accumulated stress is not completely released but instead rapidly increases to the point where tape breakage or creases occur. At the same time the tape tends to be transported towards the pressing pad 6 or the reels 2 and 3, and as a consequence a signal recorded on the track becomes abnormal. Also the tape is forcibly subjected to one sided correction in the width direction by the guide plate 9 or the like when the former is reeled on the reel 2 or 3 to increase the back tension.